Dispensing of a diagnostic liquid onto a diagnostic reagent

ABSTRACT

Biological fluid samples are deposited by methods that produce a uniform layer of the sample over a reagent-containing surface. In one embodiment, a nozzle having multiple openings is used to deposit a sample over the reagent-containing surface simultaneously. In an alternative embodiment, single droplets of the sample are deposited in a pattern on the surface, preferably in a sequence of parallel lines. The reaction between the biological sample and the reagents is read from a spectrographic image of the reagent-containing surface obtained by optical methods.

FIELD OF THE INVENTION

This invention relates to reagents and instruments used to measure thequantity of analytes in biological samples by the reaction of theanalytes with reagents to produce an optical response.

BACKGROUND OF THE INVENTION

Many instruments have been developed to measure the quantity of analytesin various biological samples, for example urine, blood, salvia, orextracts of mucus or tissue. Typically, a sample liquid is applied to asurface containing reagents that react with the analyte. The reagentsproduce a detectable response that is measured and related to the amountof the analyte. The surface can be hydrophilic or hydrophobic in nature,e.g. filter paper compared to polystyrene. Some devices usecombinations, such as urinalysis strip tests that use hydrophilic filterpaper pads on top of a hydrophobic polystyrene handle. In the typicaltest, a strip containing reagents is dipped, i.e. fully immersed in aliquid sample, and the reaction between the analyte in the sample andthe reagents is measured, typically by optical methods. Other devicesinclude microchips that use hydrophilic substrates connected tocapillaries molded of polystyrene. The reagents themselves can be watersoluble or insoluble and dried onto the supporting surface, as in teststrips. Or, they could be added as a liquid to a microchip. Additionalliquid reagents can be applied to the surfaces already containing driedreagents. Typically this application occurs after a sample has beenapplied. The sample volume should be as small as possible for obviousreasons relating to cost and convenience. What is less obvious is thatit is often difficult to obtain uniform and accurate responses whenapplying small amounts of liquid reagents or biological samples tosurfaces containing reagents.

Most biological samples and liquid reagents will have a significantwater content and thus will be compatible with hydrophilic substratesand incompatible with hydrophobic surfaces. The samples and reagentliquids when dispensed spread rapidly across hydrophilic substrates andare repelled by hydrophobic substrates. The contact between thedispensed liquid and the reagents on the surface can be made bycapillary action or directly. However, when substrates are relativelyhydrophobic, the dispensed liquid will form beads on the surface of thesubstrate that attempt to minimize their contact with the surface.Dispensed liquids therefore do not spread uniformly over the reagent.Another difficulty associated with dispensing liquids is that the driedreagents may be either water soluble or water insoluble in nature. Theinsoluble dry reagents may not be readily accessible to the liquidsamples, or soluble reagents may be dissolved and move with the liquidon the substrate. The reagents ideally should contact the sampleuniformly since the measurable response of the reagents to the sample,e.g. color development, should be uniform in order to obtain an accuratereading of the analyte in the sample.

Another problem related to obtaining good contact between a dispensedliquid and a reagent on a surface is related to the physical nature ofthe samples. They vary in their physical properties such as surfacetension, viscosity, total solids content, particle size and adhesion.Therefore they are not easily deposited in consistent volumes uniformlyover the reagent-covered substrate. Also, as the amount of the liquidsample is reduced, it becomes increasingly difficult to apply aconsistent amount of a sample with varying properties to the reagents.In contrast, ink-jet printing and the like rely on liquids developed forsuch uses and having consistent physical properties.

Deposition of droplets of liquid is a familiar operation. Examplesinclude the ink jet-printer, either piezoelectric or bubble actuated,which forms print from the controlled deposition of multiple smalldroplets of about 2 to 300 μm diameter (typically 50 μm) containing froma few femtoliters to tens of nanoliters. Other methods of depositingsmall droplets have been proposed, which generally employ piezoelectricprinciples to create droplets, although they differ from typical ink-jetprinters. Examples are found in U.S. Pat. Nos. 5,063,396; 5,518,179;6,394,363; and 6,656,432. Deposition of droplets of larger dropletsthrough syringe type pipette is known to be reproducible in diagnosticsystems from 3 to 100 μL. This corresponds to single droplet diametersof about 2 to 6 mm. A commercial example of such pipette systems is theCLINITEK ALTAS® urinalysis analyzer. The droplet size can be greater orless than the nozzle size depending on the nozzle shape, pump type andpressures applied.

The problems discussed above are particularly observed when a liquidsample is dispensed as droplets onto a reagent-containing pad. Theapplicants found that the interactions of the pad's surface and thereagents were creating inaccurate responses when the sample was added asa droplet, rather than completely covering the reagent pad by immersingthe reagent pad (dipping it) into the sample liquid, as is frequentlydone. Large droplets on the order of 3 to 100 μL do not transfer intothe reagent when the substrate is too hydrophobic and form a bubble onthe surface. They overwhelm the reagent with excess fluid if the surfaceis hydrophilic. Smaller droplets, of a few femtoliters to tens ofnanoliters, can also be a problem when deposited on a substrate that istoo hydrophobic as they lack the volume to completely cover the surfacearea and will randomly aggregate in non-uniform patterns. Small dropsalso allow open spaces for migration of water-soluble reagents. Thesetiny droplets are also prone to evaporation of liquids and to formationof aerosols, which are considered to be bio hazardous if comprised ofurine or blood specimens. Thus, if a liquid is to be deposited asdroplets on test pads, rather than dipping the pads in the sample,improvements are needed.

After contact between dispensed liquids and reagents is complete, theresults may be read using one of several methods. Optical methods arecommonly used, which rely on spectroscopic signals to produce responses.Results must be reproducible to be useful. Optical measurements areaffected by the reagent area viewed and by the time allowed for thedispensed liquids and reagents to react. Formation of non-uniform areaswithin the field of view and changes in the amount of reaction timeneeded increase errors. For example, a measurement made of a sample orreagent which has spread non-uniformly across the substrate gives adifferent result each time it is read.

It is always an objective of those who develop and improve methods ofanalyzing biological samples to provide accurate and consistent results.The present inventors propose new methods for improvement in the resultsobtained when liquid biological samples or liquid reagents are depositedon surfaces containing dried reagents, particularly when the sample isdeposited as droplets.

SUMMARY OF THE INVENTION

The invention includes methods of depositing biological fluids andliquid reagents (“liquids”) uniformly onto surfaces having an areacontaining reagents (“reagent area”) that react with an analyte in thebiological fluids and apparatus for carrying out such methods. Theoptical response resulting from the reaction of the analytes inbiological fluids with the reagents is viewed as a spectroscopic imagethat can be examined in pre-defined regions of the image.

A biological fluid or liquid reagent is dispensed using a nozzlepositioned close to the reagent-containing surface, e.g. 1-5 mm from thesurface. The liquid is dispensed as droplets having an average diameterof about 0.1 to 2.0 mm (100 to 2000 μm) and an average volume rangingfrom microliters to nanoliters. The reagent area, or an area adjacent tothe reagent area, is covered with dispensed liquid and the resultingreaction is read by optical methods within a predetermined region of thereagent-containing area as a function of the time needed for thereaction of the dispensed liquid with the reagent-containing surface.The entire reagent-containing surface maybe covered at one time, oralternatively it may be covered in a predetermined pattern of dropletsin a sequence that reacts uniformly with the reagent.

In one embodiment, multiple openings in a nozzle dispenses multipledroplets simultaneously to cover a predetermined region of the reagentarea (see FIG. 1). Each opening in the nozzle has a diameter of about0.1 to 1.0 mm and is capable of producing droplets of about 50% to 200%of the diameter of the opening. The nozzle openings are arrayed so as tocover a predetermined region area of the reagent area. Thus, nozzleopenings are sufficient to cover the predetermined region on the surfaceeither simultaneously or in multiple passes, which may be done by movingthe droplet-dispensing nozzle or the reagent-containing surface, orboth.

In a second embodiment, one opening in a nozzle dispenses droplets (seeFIG. 2). The opening in the nozzle has a diameter of about 0.1 to 1.0 mmand is capable of producing droplets of about 50% to 200% of thediameter of the opening. A pattern may be formed by traversing thereagent-containing surface in a predetermined sequence of lines, e.g.about 1 to 100 passes across the reagent surface, by moving thedroplet-dispensing nozzle or the reagent-containing surface, or both.

In a third embodiment, the biological fluid or liquid reagent isdispensed by either single or multiple hole nozzles onto the surfaceadjacent to the reagent area such that the droplets are uniformlytransferred into the reagent-containing area by capillary action (seeFIG. 3). The dispense pattern may be formed by traversing the surface ina sequence of lines, e.g. about 1 to 100 passes across the reagentsurface.

In other embodiments, a liquid reagent (or reagents) are applied to thereagent area, either before, after, or with the deposition of thebiological sample. Preferably, the liquid reagent is applied after thebiological sample has been dispensed.

Exposing the reagent-containing area to a light of a suitable wavelengthprovides information on the reaction that occurs between the analyte inthe biological sample and the reagents in the form of a spectrographicimage that is read in predetermined regions of the image to moreaccurately measure the amount of the analyte in the biological sample.The predetermined regions may be the entire reagent-containing area,portions thereof, or the area covered by a singled droplet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sectional view of a multiple hole nozzle dispensingliquid droplets in a first embodiment of the invention.

FIG. 2 shows a sectional view of a moving nozzle dispensing liquiddroplets in a second embodiment of the invention.

FIG. 3 shows a sectional view of a nozzle and a liquid in the thirdembodiment of the invention.

FIG. 4 shows the spread area of dispensed liquid on a highly hydrophobicreagent surface.

FIG. 5 shows the spread area of dispensed liquid on a highly hydrophilicreagent surface.

FIG. 6 shows the optical scan of a dispensed liquid as a function oftime and drop size.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Definitions

The following terms used herein are defined as follows:

“Spectrographic image” refers to a detailed view of the optical responseof a reagent-containing area to a biological sample deposited on thereagent-containing area, which enables examination of sub-units of theentire reagent-containing area.

“Hydrophilic” surfaces are those that have a less than 90° contact anglebetween the surface and a drop of water placed thereon.

“Hydrophobic” surfaces are those that have a 90° or larger contact anglebetween the surface and a drop of water placed thereon.

“Figure of Merit (FOM)” is a calculated measure of performance in whichthe mean difference between results obtained from samples with andwithout an analyte present is divided by the square root of the sum ofthe squares of standard deviations, the results comparing sampleswithout the analyte and samples containing the lowest analyteconcentration that can be detected.

The objective achieved by the methods of the invention is to cover areagent-containing surface with a uniform layer of a liquid to obtainimproved accuracy of results. Each portion of dispensed liquid contactsthe reagent-containing surface and makes direct contact to acorresponding portion of the reagents, so that the reaction of theanalyte in each portion of the sample occurs where the liquid wasdeposited. As will be seen in the discussion that follows, typicalreagent-containing surfaces may not be well suited for dispensing ofdroplets because of their hydrophobic or hydrophilic properties relativeto the biological sample with which they are to react.

Dipping a reagent-containing surface in a liquid sample achievescomplete and uniform contact with the reagents. The present inventionaccomplishes similar results without the need for immersing thereagent-containing surface and provides several advantages. First, bydispensing droplets, rather than dipping the reagent-containing surface,less sample is needed and the amount of dry and liquid reagents requiredis generally reduced. Second, manual steps such as adding liquidreagents by hand, can be eliminated. Also, automated analysis, in whichsmall test areas are placed on a card or strip, becomes easier toimplement. Either the card or strip or the nozzle can be moved to permitmultiple tests of a single sample liquid or a single test of multiplesamples. This results in being able to dispense on demand to reagentareas of interest.

Of particular importance to the invention is the improved accuracy andprecision (repeatability) that can be obtained over standard pipettesystems. The improved accuracy and precision results from being able toread the results of the response of the reagents to the sample byviewing a focused spectroscopic image across the entire reagent area asa function of time and position. A particular benefit of the small dropsizes used in the invention (in the range of 0.1 to 1 mm diameters) isthat they are readily absorbed by very hydrophobic surfaces, while largedrop sizes are not. An additional advantage of the small drop sizes isthat patterns can be dispensed that allow using reagents-containingcards without carry-over between adjacent reagent areas.

Effect of Reagents on Liquid Absorbed

A series of tests was carried out to demonstrate the impact ofdispensing on accuracy and precision of the measurements made of thereaction of a biological sample with reagents. Reagents from theMULTISTIX® products (Bayer) were tested with CHEKSTIX liquids (Bayer) orother standardized test solutions containing and lacking analytes to bedetected. Some of the reagent surfaces were hydrophobic while otherswere hydrophilic. Some of the reagents tested were water-soluble whileothers were water-insoluble (see Table 1). In all cases the reagentscontained on a porous pad of bibulous (i.e. absorbent) material placedon top of a non-porous polystyrene film as a substrate.

In a first test, the typical performance of reagents was established bydipping (immersing) a fixed area (5×5 mm) of the reagent-containing padinto an aqueous test sample. The maximum volume of liquid absorbed bythe reagent surface after dipping was determined by the change in weightof the fixed area. In a second test, a pipette was used to dispense thissame maximum volume as large droplet sizes (1.7 to 20.4 μL) onto thereagent surface. The performance of reagents after dispensing the largedroplet sizes was measured by a CLINITEK STATUS® urinalysis strip readerand compared to the performance when dipped (see Table 2). In a thirdtest, a micropump with a single nozzle was used to dispense a series ofsmall droplets sizes (100 nL to 1 uL) onto the reagent surface (FIG. 1).Again, the performance of reagents after dispensing the small dropletsizes was measured and compared to the performance after dipping (seeTable 2).

The performance of reagents was measured as a Figure-of-Merit (FOM)using the response to a series of test samples that either lacked orcontained the analyte being measured. Figure-of-Merit (FOM) wascalculated as the absolute difference between the mean results for twotest samples lacking and containing a low concentration of the analytedivided by the square root of the sum of the squares of standarddeviations observed at each level. Higher values of FOM are preferred,but for the present tests, a value of at least 7-10 indicates acceptableperformance. Figure-of-Merit (FOM) values were calculated for dippedreagents and for reagents that had the sample liquids dispensed as largeand ideal droplet sizes (see Tables 1 and 2).

TABLE 1 The performance of reagent surfaces after dipping in testliquids. Volume of Surface energy Water solubility Reagent for sample(μL) of reagent pads of reagents FOM Urobilinogen 7.4 HydrophilicInsoluble 10.1 Occult blood 7.4 Hydrophilic Insoluble 15.3 pH 7.4Hydrophilic Insoluble 21.0 Protein 8.3 Hydrophilic Soluble 38.0Creatinine 6.5 Hydrophilic Soluble 13.9 Bilirubin 14.1 HydrophilicSoluble 28.1 Specific 9.5 Hydrophilic Insoluble 13.5 gravity Nitrite20.4 Hydrophilic Very soluble 19.9 Leukocyte 17.0 Hydrophilic Verysoluble 12.1 Ketone 6.5 Hydrophilic Very soluble 11.3 Albumin 8.3Hydrophobic Insoluble 13.0 Glucose 1.7 Very Insoluble 19.2 HydrophobicPolystyrene 0.2 Very NA NA without reagent Hydrophobic

Pipetting Droplets Compared to Dipping

It was evident that reagent-containing pads absorbed varying amounts ofliquid when dipped depending on the composition (Table 1). In general,very hydrophobic reagent surfaces absorbed less liquid. The veryhydrophobic polystyrene surface having a surface tension of 70 dynes/cm²held a film of only 0.2 μL. A significant variation in the amount ofliquid picked up was found among dry reagents of similar surface energyand affected by the reagent ingredients.

In additional tests using a pipette to dispense relatively largedroplets of samples (1.7 to 20.4 μL) did not provide as uniform responsefrom the reagents as desirable (see Table 2). The FOM values for largedroplets were lower than FOM values for dipping. FOM values are smallerwhen the difference between the results with and without an analyte inthe sample is small and the standard deviation is large. Therefore,accuracy and consistency of the measurements of the analyte in a sampleliquid were worse when large droplets were used. There are severalreasons for the poor performance. Large droplets could not give aresponse for the very hydrophobic reagents (e.g. glucose) as thedroplets did not enter the porous pad and make contact with the dryreagent. Droplets formed a ball on the surface of the reagent and didnot spread (See FIG. 4 in which the diameter of the drop did notincrease as liquid was added). Another reason was that large dropletsapplied to reagents with water soluble liquids (e.g leukocyte) have poorresponse compared to dipping because the reagent migrates as the dropspreads across the surface. The large droplets produce excess liquid onthe porous pad by overwhelming the water absorbing capacity, resultingin migration. This also increases the probability that carry-overcontamination will occur between dry reagent areas that should receiveseparate liquid samples. A final reason for poor performance of largedroplets was observed in hydrophobic surfaces with water insolublereagents (albumin). In this case poor absorption of the dispensedliquids generates uneven applications and non-uniform signals.

Generally, droplets were applied to the middle of each pad. The liquidcoverage observed depended on the droplet size (see FIG. 5 in contrastwith FIG. 4) and the total volume applied. It was found that the amountto fill the reagent pad with liquid by pipette was often less than thatfound by dipping. Generally, about 6-8 μL of total liquid volume wasneeded to reach agreement performance between pipetting and immersion inthe test solution. It was concluded that achieving equivalentperformance when depositing sample liquids in droplets, compared withdipping, required precise deposition of the sample. Ideal liquid volumesdispensed by droplets were selected based on the best FOM achieved(Table 2). When small droplets were deposited, multiple drops were usedto achieve the ideal total volume. It was concluded that, depending onthe properties of the test pad, the volume of liquid deposited asdroplets should be varied to assure equivalent performance. When thiswas done the FOM achieved with small droplet sizes equaled or surpassedthe performance of dipping for all reagent surface types (compare Table1 and 2).

TABLE 2 The performance of reagent surfaces after depositing droplets oftest liquids. Small droplets sizes Large droplets sizes (100 nL to 1 uL)(1.7 uL to 20.4 uL) Observation Reagent for Observation FOM absorptionFOM Urobilinogen Absorbed 9.8 Absorbed 11.2 Occult blood Absorbed 14.9Absorbed 17.3 pH Absorbed 22.0 Absorbed 36.5 Protein Overly absorbed 3.5Absorbed 41.2 Creatinine Overly absorbed 8.4 Absorbed 14.1 BilirubinOverly absorbed 3.4 Absorbed 27.6 Specific gravity Absorbed 9.6 Absorbed13.3 Nitrite Overly absorbed 6.1 Absorbed 22.3 Leukocyte Overly absorbed2.3 Absorbed 15.3 Ketone Overly absorbed 8.4 Absorbed 12.1 AlbuminPoorly absorbed 6.3 Absorbed 10.6 Glucose Not absorbed 0.1 Absorbed 10.6

Effect of Volume and Drop Size and Dispense Pattern

In addition to the need to correlate the performance of results obtainedwhen pipetting sample liquid onto a reagent pad with the volume ofliquid, it is also important to determine how the volume depositedaffects the spreading of liquid. A study was undertaken to evaluate theeffect of increasing the amount of liquid droplets on the spread of theliquid on a hydrophilic surface and a very hydrophobic reagent surface.It was found that as the droplet size was increased, the diameter of theliquid on the hydrophilic reagent pad increased (see FIG. 5), as mightbe expected. But, in the case of a very hydrophobic reagent pad(Glucose) little absorption and expansion of the liquid occurred whenlarge droplets were used (see FIG. 4). However, it was surprising tofind that when the droplet size was under 100 nL, the liquid wasinstantaneously absorbed and expansion occurred (relative to the size ofthe droplet). That is, when the droplets are small, the hydrophobicreagent pad behaves as if it is hydrophilic. It was concluded thatdeposition of multiple smaller droplets would be preferred to provideuniform coverage. Also, by controlling of the sample volume, moreefficient use of the available reagent pad should be possible.

Problem of Hydrophobic Surfaces

When a reagent pad is very hydrophobic, for example the glucose pad usedin these tests, it is difficult for the liquid sample to penetrate thepad with large droplets. (Note the results of the tests on liquidabsorption in FIG. 4). In the glucose pad, this may be doneintentionally to limit the entry of the sample liquid. The color changefrom the reaction of glucose in the sample with the reagents only occurswhere the liquid touches the surface under the base of a drop sitting onthe surface. Therefore, it would be preferred to deposit many smalldroplets over a defined area in order to obtain the best results, ratherthan to pipette large droplets. When this is done the performance equalto or greater than that of dipping can be achieved (Note the FOMachieved with small droplets in Table 2).

Depositing Onto Reagent-Containing Areas

FIG. 1 illustrates a first embodiment of the invention, in which anozzle 12 a is supplied from liquid chamber 10 a and multiple nozzleopenings dispense droplets 14 a onto a reagent-containing area 18 a,which is supported on a hydrophobic surface 16 a.

FIG. 2 illustrate a second embodiment of the invention, in which anozzle 12 b is supplied from liquid chamber 10 b and a single nozzleopening dispenses droplets 14 b onto a reagent-containing area 18 b,which is supported on a hydrophobic surface 16 b. In this embodiment thenozzle is moved or the reagent-containing area is moved relative to thenozzle to deposit droplets in a predetermined pattern.

A liquid can also be dispensed onto a very hydrophobic substrate, forexample a portion of a polystyrene substrate that is offset from thereagent area. This is a third embodiment of the invention, illustratedin FIG. 3. A liquid chamber 10 c supplies nozzles 12 c that dispensedroplets 14 c to the hydrophobic surface 16 c adjacent to areagent-containing area 18 c. The liquid sample will migrate to thereagent containing area via capillary action. Capillary action can beachieved either by capillaries in the polystyrene leading the fluid tothe reagent or by capillaries in the reagent area wicking the liquid in.With large droplets, liquid contact is poor. Droplets larger then thecapillaries, either in the reagent or in the polystyrene, do nottransfer into the reagents; the droplets instead form a bubble.

In two test cases, one large droplet of 4 uL and 40 small droplets of0.1 uL were applied to polystyrene off-set from the glucose reagentarea. In a first case, test droplets were placed in contact with a microcapillary of 150 by 100 microns by 4 mm long that was in contact withthe glucose reagent area. The large droplet was not transported throughthe capillary in 60 seconds while the smaller droplets moved through thecapillary and into the reagents with in a few seconds. Therefore aresponse was measurable only with the small droplets. In a second case,test droplets were placed in contact with the capillaries inside glucosepad. The large droplets were reluctant to migrate into the pad in lessthan 60 seconds. As the pad contained many capillaries some migrationoccurred. The smaller droplets readily entered the pad. The FOMdetermined for the large droplet case was <3, while the FOM for thesmall droplet case was 22.1, demonstrating the performance advantage forsmall droplet application. Similarly improved results were obtained forsmall droplets when the glucose reagent was replaced with affinitymembranes containing immunoassay reagents for detecting hCG, hbAlc andUristatin.

Problem of Water Soluble Reagents

When water-soluble reagents are in the reagent surface, the sampleliquid, e.g. urine, absorbs them. Then, as the liquid spreads on thereagent area, the water-soluble ingredients move with the liquid at thesolvent front. This migration creates a non-uniform color development.Tests with water-soluble ingredients were used to measure migration. Theleukocyte reagent (containing water-soluble ingredients) tested withlarge drops indicated substantially the same results, regardless of thesample volume and whether the sample contained leukocytes or not (FOM of<3, Table 2). However, when the test pads were dipped in the sampleliquid or the liquid was applied in small droplets, the presence orabsence of leukocytes was readily determined (FOM of >10, Tables 1 or2). Spreading of water soluble ingredients was apparent in eitherdipping or small droplet application. Simultaneous coverage of thereagent surface with repeated application of small droplets limited themigration and made any migration that occurred a predictable pattern. Inthe case of large droplets, (>3 uL) random aggregation causednon-uniformity in the migration. In the case of very small droplets (<10nl), random aggregation also occurred along with evaporation. Thiscreated not only non-uniform migration but also open spaces lackingdeposited liquid.

In one possible application, since spreading of the liquid is limited bythe droplet volumes and spraying patterns onto the reagents areas,multiple test areas can be defined on a continuous surface of reagent(e.g. a long ribbon of reagent or a card of polystyrene containing sucha ribbon) that is fed under the dispensing nozzle. The hole spacingcould be adjusted to allow sufficient separation between individualreagent areas without liquid communication between the discrete reactionareas. The hole spacing also could be adjusted to provide a uniformresponse from the reagents and to avoid migration of water solublereagents. In test cases, it was shown that droplets of 1 uL and less canbe separated on a 5 mm by 6 in ribbon of reagent by properly spacingdispense patterns. The results were read by an optical read headpositioned to direct light over the test area and to receive reflectedlight at a predetermined time after the sample liquid has been sprayedon the test area.

Properly Spacing Dispense Patterns

In a typical embodiment, the nozzle will be spaced about 5 mm or lessabove the reagent surface. In FIG. 1 to 3 the nozzle plate has beendrilled with holes so that the droplets fall vertically onto the testarea. The plate may also be curved with the droplets falling at anangle. To minimize cross contamination the distance between the nozzleand the test area will be as small as possible, typically greater than 1mm and less than 5 mm for accurate droplet placement, as determined bythe size of the droplets and their trajectory.

As demonstrated with ribbons, precisely depositing liquid makes itpossible to space test areas closely on a substrate containing reagents,while avoiding cross-contamination. The number and size of the nozzleopenings will vary depending on the application, but holes should begreater than 100 μm diameter, to avoid creating an aerosol. Since thenozzles will be sized to dispense droplets over a given size test area,it will normally be the case that the nozzle will be roughly the size ofthe test area as a minimum or much smaller when using multiple holes ormultiple passes over the test area. The test area of course will besmall, say about 1 to 25 mm square, and have any desired shape, althoughsquares or circles are most common. Since the nozzles of the inventionprovide accurate placement of the sample liquid, the test areas can beclosely spaced, thus improving efficiency and accuracy of the analysis.Depending on the water solubility of reagents, it was observed that thetest areas could be spaced as close as about 1.3 to 10 mm (from centerto center) with only about 0.3 to 8 mm between adjacent edges.

Relationship of Droplet Pattern to Optical Image

When this method of dispensing a small droplets onto a reagent area isadopted, it is possible to improve the method of reading the opticalresponse to the reagents to the sample. In the conventional technology,the response of the reagents e.g. color development, is determined forthe entire reagent area by supplying light having the desiredwavelengths to the area and measuring the returned or transmitted lightto a photo detector. The amount of light measured is correlated with theamount of the analyte in the sample that has reacted. In effect, anaverage of the color developed over the reagent area is read. A moreaccurate measurement would luminate the reagent area in a pattern andmanner corresponding to the deposition of the sample liquid. That is, alight beam could traverse (scan) the reaction area and the returned ortransmitted light could be received and measured, one spot (pixel) at atime. Such a process could be thought of as being analogous to thepattern traced on the screen of a cathode ray tube in a conventionaltelevision set. This is illustrated in FIG. 6 a, in which light fromlight source 1 is directed (2) to a reagent surface 3. Reflected light 4passes through a lens 5 and is detected by camera 6. The spectrographicimage 7 is reported as shown in FIG. 6. Area 9 shows the region in whichthe reflectance is high while area 8 shows the region where reflectanceis low.

As a result, a scanned spectrographic image can be obtained atpredetermined times to provide spectral information at various pixelpositions across the reagent surface. FIG. 6 shows the spectrographicimage across a reagent surface in the x-direction. In FIG. 6, ten pixelsequals 1 mm, so the width being examined is 10 mm. The results could beaveraged across the selected scan area and reported as the total colordeveloped, which would then be related to the analyte present in thereagent area. The scanned image was found to be dependent on time anddrop size. The larger droplet size (“C”) (8 μL or 2.5 mm diameter)formed even more uneven patterns when the reagents contained watersoluble ingredients due to migration at the solvent front as previouslymentioned, resulting in lower reflectance at the outer edges of thedroplets. The smaller droplet size (“A and B”) (20 droplets of 0.5 μmdiameter) formed even more patterns with the same reagent, providedenough time was allowed for reagents to react. Curve A shows thedroplets soon after being dispensed; Curve B shows the spread at a latertime. This method of reading the optical response of the reagents isparticularly well suited to the dispensing of individual droplets intraces that cover the area, but it could also be used with theembodiment of the invention in which a spray nozzle is used, asdescribed above.

Lower Limit of Droplet Size

The droplet size limit of 100 nL was chosen to accommodate urine as asample liquid, which includes particulates (e.g. cell, casts, crystal,bio-molecules and the like) that affect the ability of the nozzle holesless than 100 um to deliver consistent size droplets. It was furthershown that hole diameters greater than 100 μm allow sufficientseparation to flush out particulates and to prevent carry-over crosscontamination. Since the total sample liquid will be equivalent to thatdelivered as a single droplet by a pipette, about 1 to 1000 smalldroplets are delivered over a short period, say about 0.2 to 5 seconds,the nozzle hole is used repeatedly and must not clog. The desired resultwas that hole diameters greater than 100 μm allowed thousands of smalldroplets are deposited uniformly over the reaction area to provide auniform response from the reagents. Additional problem observed withhole diameters smaller than 100 μm were evaporation of liquid beforeabsorption was completed and the formation of aerosols.

More generally, it is believed that droplets of less than 100 μmdiameter could be used when the fluid is a liquid reagent withoutparticles and the dispense height is close to the reagent surface.

Nozzle Arrays

The nozzles may be supplied with sample fluid or reagent under pressurefrom a source, which may be for instance, a syringe pump, diaphragmpump, pressurized container, piezo actuator, diaphragm, peristaltic,vortex, suction, centrifugal and the like with or without check-valves,splitters, air supply and venting

Many arrangements are contemplated within the scope of the invention. Itis expected that the nozzles will be used in automated analyzers whereadvantage can be taken of their superior coverage of the test area. Forexample, more than one nozzle could be used, arranged in groups of 1 to20, supplied by 1 to 20 liquid sources, either individually or ingroups. The nozzles could be supplied and replaced individually or ingroups. Since the nozzles may require replacement after depositing 100to 1000 samples, either for cleaning or for disposal, they would belikely made in groups that are easily removed and replaced.

In another embodiment, the entire reagent area is not coveredsimultaneously with sample liquid by deposition from a nozzle containingmany openings. Instead, the reagent area is covered with small droplets,one at a time, tracing out patterns in the reagent area. This process isanalogous to the ink jet printer in that droplets are deposited inlines, but rather than forming characters separated by spaces free ofink, the present process covers substantially all of the reagent areaand assures that all of the reagents react with the sample and asuniformly as possible. Depositing droplets in this matter requiresmovement of the depositing nozzle (or nozzles) or the reagent area, orboth. Preferably, the reagent area is moved under a stationarydispensing nozzle (or nozzles).

In a typical reagent area of about 25 mm² a series of traces could bedeposited beginning at one edge and proceeding in parallel traces untilthe opposing edge is reached. The width of each trace may vary dependingon the size of the droplets and the spreading of each droplet after itlands on the reagent area. For example, with droplets having a diameterof 100 to 1000 μm, the reagent area of 25 mm² would be covered withabout 50 to 5 linear traces, for a total of about 2500 to 25 droplets.The process would be carried out in only about 0.01 to 2 seconds. Otherpatterns could be used to cover the entire reaction area, such as acircular trace beginning at the center of the area and moving outward ina spiral until the outer edge of the area is reached.

In two embodiments, the present invention includes the substitution of anozzle with one or more small holes (FIGS. 1 & 2) having diameters ofabout 100 to 1000 μm. Since individual dry reagent areas that aretypically used for analysis are small, say about 1 to 25 mm square, thenozzle includes enough openings cover a measurable amount of the reagentsurface with small droplets in as few passes as possible. As these smalldroplets require nozzle holes of about 100 to 1000 μm in diameter, thenumber of holes may range from 1 to 10 for every mm² surface to becovered by the nozzle.

In addition to using single nozzles, other possible arrangements includemultiple nozzles, each one supplied from one or more containers for theliquids to be dispensed. The nozzle or nozzles could be moved from onetest area to another, or the test areas could be moved under stationarynozzles. In one arrangement, multiple nozzles are used to dispensedifferent liquid samples onto reagents. For example, to be useful in theClintek Atlas®, an automated urine analyzer (Bayer Corporation), anozzle must be arrayed to dispense over 40 separate urine samples ontoat least 12 reagents. The nozzle container also must be washable betweensamples. Alternatively, an array of nozzles with separate containerscould be used, with each dispensing a separate sample or with eachdispensing the same sample onto separate test areas.

Adding Reagents

In more conventional technique reagents are added to a bibulous surfacee.g. an absorbent pad, and then dried. The biological fluid sample isadded and after sufficient time has elapsed for color or other opticalresponse to develop, the reagent-containing surface is read andcorrelated with the amount of an analyte in the sample. In the presentinvention the precise deposition of the biological sample and thespectroscopic imaging of the reagent area makes it possible to depositadditional reagents as desired at the time the biological sample isbeing tested.

In one embodiment of the invention, after the biological sample has beendeposited on the reagent area, an additional reagent (or reagents) isdeposited on all or selected portions of the reagent area.

Alternatively, or additional reagent (or reagents) could be depositedbefore the biological sample is placed on the reagent area. This couldserve to activate other reagents already in place, for example, or toadd a reagent having a short shelf life that could otherwise not beused.

In still another embodiment, the additional reagent (or reagents) couldbe added simultaneously with the biological sample. This method couldprovide mixing needed for lysis of cells, affinity reactions, chemicalreaction and dilutions.

Depositing Liquid Reagent After the Sample

A liquid can be dispensed onto a reagent area after the sample has beenadded. For example, 3 μL of urine was added to the glucose reagentfollowed by 3 μL of phosphate buffer pH 6.5. The urine sample madeliquid contact with the reagent at 0 seconds and the color reaction isstarted. The liquid buffer makes liquid contact with the reagent 10seconds later and the color reaction continues. The FOM is reduced whenhigh specific gravity urine is used as the sample as the glucose reagentresult is inhibited by high chloride content in the sample. Withapplication of a secondary liquid reagent after the sample, variationsbetween the low and high sample are reduced and the FOM is improved dueto the lowered dissolved salt in the diluted sample, as shown in Table3.

TABLE 3 The performance of glucose reagent surfaces after dispensingsample followed by test liquids. Small droplets sizes Small dropletssizes without secondary with secondary liquid reagent liquid reagentObservation Observation Glucose sample absorption FOM absorption FOM lowSG urine Absorbed 10.6 Absorbed 12.2 high SG urine Absorbed 5.4 Absorbed11.3

1. An apparatus for dispensing a uniform layer of droplets from a sampleof a biological fluid from at least 1 mm above a surface containingreagents for reacting with said reagents comprising: (a) a nozzle fordispensing said sample of a biological fluid, said nozzle having aclosed channel ending in one or more openings having diameters greaterthan 100 μm and up to about 1000 μm for dispensing under pressure saidsample of biological fluid as droplets having diameters in the range of0.1 to 2 mm onto a predetermined region of said reagent-containingsurface; (b) a reservoir for supplying said biological sample to saidnozzle of (a); (c) automated means for positioning said nozzle withrespect to said reagent-containing surface or said surface with respectto said nozzle such that said nozzle is positioned at least 1 mm abovesaid reagent-containing surface during dispense such that the dropletsfall onto the reagent-containing surface; (c) means for dispensing underpressure said biological sample via said nozzle openings ontopredetermined portions of said reagent-containing surface; and (d) meansfor reading the results of the reaction between said biological fluidand said reagents from a spectrographic image of the reagent-containingsurface.
 2. An apparatus of claim 1, wherein said predetermined regionof said surface is the entire reagent-containing region.
 3. An apparatusof claim 1, wherein said predetermined region of said surface is thearea contacted by one droplet dispensed by said nozzle openings.
 4. Anapparatus of claim 1, wherein said predetermined region of said surfaceis a portion of said surface containing reagents.
 5. An apparatus ofclaim 1, wherein said means for reading the results of the reactionbetween said biological fluid and said reagents includes a source oflight directed onto a predetermined portion of said spectroscopic imageand a detector for measuring the light returned from said portion ofsaid spectroscopic image.
 6. An apparatus of claim 1, wherein saidpredetermined region of said spectroscopic image consists of the entirereagent-containing surface.
 7. An apparatus of claim 1, wherein saidpredetermined region of said spectroscopic image consists of the areacontacted by one droplet.
 8. An apparatus of claim 1, wherein saidpredetermined region of said spectroscopic image consists of a portionof said reagent-containing surface.
 9. An apparatus of claim 1 furthercomprising means for dispensing reagent liquids onto saidreagent-containing surface through the one or more openings in saidnozzle.
 10. An Apparatus of claim 1 wherein said nozzle dispensesdroplets under pressure when said nozzle is positioned from 1 to 5 mmabove said reagent-containing surface.